When Mitt Romney defeated Barack Obama in their first presidential debate last week, and by common consent that’s what happened, he raised the pressure on Joe Biden to even the score in the vice presidential debate tomorrow.

Biden will have a tough time doing that. Even though Republicans will be trying to lower expectations for their candidate, Rep. Paul Ryan, everyone knows he is a formidable and unflappable debater. He knows the ins and outs of domestic policy at least as well as Biden, and speaks more authoritatively about them. Ryan has also spent more elections having to win voters outside his party. What’s more, Biden has some predilections that will make his own job harder.

Biden seems to believe — judging by how he goes on about it — that he has some special gift for connecting with middle-class voters. This may lead to overconfidence. Ryan’s been at least as effective as Biden in making a blue-collar case for his party’s ideas.

The Democratic reaction to Obama’s debate loss may also point Biden in the wrong direction. Among liberals — and among some Democratic strategists, too — the prevailing view is that Obama lost because he didn’t call Romney on his outrageous lies, and especially because he didn’t draw a stark contrast on Medicare and Social Security. Obama even said the two candidates had a “similar position” on the second program. Democrats will be urging Biden to be more combative.

The vice president isn’t above demagogic attacks: In his convention speech, he claimed “experts” had said that one of Romney’s tax proposals would create 800,000 jobs, “all of them overseas, all of them.” In fact, Biden was referring to a study by one expert, and it didn’t say what he claimed: It estimated 800,000 jobs would be created overseas, but it didn’t examine the impact domestically.

Yet Biden also likes to be liked, and has tended to take his hardest shots before partisan audiences rather than in front of the Republicans he is criticizing.

And the consensus Democratic view that Obama was too passive and disengaged probably misunderstands why he lost the debate. The real problem was that he was less up to speed on the arguments and counterarguments than Romney was. If Biden internalizes the Democratic conventional wisdom, he’ll be more engaged than Obama was — but it won’t help unless he is also better informed. An amped-up yet inadequate response can come across as bluster.

A few things may work in Biden’s favor. Obama didn’t know what to say when a Republican made an argument that differed from the straw men the president loves to create. Maybe Biden — who built closer working relationships with conservatives in the Senate than Obama ever has — will be prepared with more effective rebuttals.

Democrats also probably don’t need to worry about Biden’s penchant for gaffes. Yes, he said last week that the middle class “has been buried the last four years,” which is maybe not the ideal message for a ticket asking for four more. He also has a history of making racially insensitive remarks — about Indian-Americans as 7-Eleven owners and Obama as “clean” and “articulate.” As Ryan has pointed out, though, Biden typically makes such blunders when he is relaxed rather than in high- pressure situations, such as nationally watched debates. He didn’t say anything disastrous in his debate with Sarah Palin in 2008, and is generally thought to have won it.

Biden gave a stronger, more tightly focused speech at the Democratic convention than Obama did. He will have to do better than Obama again this week. The race is a dead heat, according to the most recent polls, and the Democrats have been running as much against Ryan as against Romney. So the stakes are higher for Biden than they usually are in vice presidential debates. It’s safe to say that Republicans are looking forward to this one more than Democrats are.